That number is a huge increase from 2000, when just a quarter of the world had myopia (the medical term for nearsightedness). However the optometrists we spoke with didn’t find the estimate surprising. “We see people with mild myopia worsening every year,” says Eric Perez, an optometrist. “We see patients with myopia that do not have a family history of it.”

Two culprits are likely to blame:

1. Increased Screen Time

Eye doctors use the term “near work,” but mostly they’re referring to the screens you look at (like right now!). As we spend more time looking at computers and smartphones that are just a few feet—and sometimes only inches—away, we don’t give our eyes a chance to look into the distance. (So now you know why you have so much trouble reading road signs.)

Fix It: Use the 20/20/20 rule, says Dominick Maino, an optometrist. Every 20 minutes, look at an object at least 20 feet away for 20 seconds. (If you use Google Chrome, you can even download eyeCare, a browser extension that reminds you to look away.)

2. Decreased Time Outdoors

When you're outdoors, you tend to look at more objects in the distance, exercising that part of your vision, Perez says. There’s also research that shows natural sunlight triggers the release of dopamine in your retina, which also helps prevent myopia.Time outdoors and the prevention of myopia. French AN, Ashby RS, Morgan IG. Experimental eye research, 2013, May.;114():1096-0007.